Dual link DVI transmitter serviced by single phase locked loop

ABSTRACT

A dual link transmitter constructed according to the present invention employs a single Phase Locked Loop (PLL) to service both a primary link and a secondary link during dual link mode operations. The structure of the dual link transmitter includes both a primary link PLL and a secondary link PLL. The primary link PLL produces a primary link clock and the secondary link PLL produces a secondary link clock. During dual single link operations, the primary link clock is used to service the primary link while the secondary link clock is used to service the secondary link. However, during dual link operations, the primary link clock is used to service both the primary link and the secondary link.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of and claims priority to U.S. PatentApplication having an application Ser. No. 10/145,411; filed May 14,2002; which application claims priority to U.S. Provisional PatentApplication Ser. No. 60/356,322, filed Feb. 12, 2002; and in which bothapplications are hereby incorporated by reference in this application.

1. FIELD OF THE INVENTION

This invention relates generally to digital communications; and moreparticularly to high-speed serial data communications.

2. BACKGROUND OF THE INVENTION

Communication technologies that link electronic devices are well knownin the art. Some communication technologies link electronic devices vianetworks. Examples of such networks include wired computer networks,wireless computer networks, wired telephone networks, wireless telephonenetworks, and satellite communication networks, among other networks.Within such communication networks, a network infrastructure coupleselectronic devices to one another. Other communication technologiessimply link one electronic device to another electronic device. Examplesof these types of links include links between computers and theirperipheral devices, links between portable data units and computers,links between video devices sources and video monitors, and linksbetween audio sources and audio playback devices, among other examples.With regard to the computer and peripheral device example, communicationlinks couple the computer to its display, the computer to its printer,the computer to its mouse, and the computer to its keyboard, amonglinks.

Many communication link applications require high data rate throughputwith minimal or no errors in the data transmitted. Some of thesecommunication links operate in a parallel fashion in which data iscarried on a plurality of physical conductors and is clocked in unison.Other of these communication links operates in a serial fashion in whichdata is carried on a single physical conductor or multiple physicalconductors from the first device to the second device in a serialfashion.

One particular type of serial link is a high-speed bit stream seriallink. In a high-speed bit stream serial link, data is transmitted from atransmitting device to a receiving device one bit at a time so that,over time, a plurality of bits of data are transferred. An example ofsuch a high-speed bit stream serial link is described generally in theDigital Visual Interface (DVI) standard promulgated by the DigitalDisplay Working Group, which is incorporated herein by reference for allpurposes. The DVI standard sets forth a high-speed bit stream seriallink that carries display information from a video source (transmitter)to a video display (receiver), in one operation. The transmitter may becontained in a computer, a cable modem set top box, a satellite receiverset top box, or another source of video content while the receiver istypically contained in a monitor that displays the visual informationreceived via the high data rate bit stream DVI serial link.

The DVI standard describes the operational characteristics of thephysical communication path between the transmitter and the receiver.The DVI standard provides for one or two DVI links, each of whichincludes a plurality of bit stream paths (data channels) that issynchronized to a clock signal (bit clock). The bit clock and bitsstreams may operate at frequencies up to 1.65 Gigahertz. At suchoperating frequencies, the bit streams traveling along the bit streampath(s) are subject to a number of operating conditions that distort thebits as they pass from the transmitter to the receiver. Distortion ofbits caused by dispersion along the conductors carrying the bit streamsis generally referred to as inter-symbol interference (ISI). ISIdistorts the bits such that extraction of the bits from the bit streamis subject to error. Further, the data bit stream(s) is/are often timesnot aligned fully with the bit clock. Misalignment between a bit streamand the bit clock typically varies over time and is referred to as bitstream jitter. Bit stream jitter often prevents the successfulextraction of bits from the bit stream. Whenever bits are not properlyextracted by the receiver from the bit stream, data is lost. However,bit stream jitter is common. In many operations, bit stream jitter makesit extraordinarily difficult to successfully meet a data rate, e.g., anerror rate of 10⁻⁹ or less.

In dual link DVI applications, six channels are supported, threechannels for a primary link and three channels for a secondary link. Thedata contained on these channels is theoretically synchronized upon itstransmission such that it arrives at a receiver in a synchronized form.However, the pair of transmitters that service the dual link DVIapplication may drift with respect to one another such thattransmissions are not synchronized with respect to one another. Further,differences in the respective transmission paths that service the duallink DVI may be such to cause the signals to be further offset from oneanother when they reach respective servicing receivers. Finally,mismatches in operation of a pair of receivers that service the duallink DVI may also introduce skew into the received data path.Resultantly, data that is received in a serial format and converted to aparallel format for each of the dual links may be skewed in time,causing errors in operation of a servicing receiver.

Therefore, there is a need in the art for a DVI transmitter thatminimizes transmission skew of data bits during dual link modeoperations.

SUMMARY OF THE INVENTION

Thus, in order to overcome the above-described shortcomings, as well asothers of the prior devices, a dual link transmitter constructedaccording to the present invention employs a single Phase Locked Loop(PLL) to service both a primary link and a secondary link during duallink mode operations. By using a single PLL to service both the primarylink and the secondary link during dual link mode operations, the datacontained in a plurality of primary link data channels are temporallyaligned with a plurality of secondary link data channels. Further, a bitclock that is produced that services both the primary link and thesecondary link is temporally aligned with the primary link data channelsand the secondary link data channels. Thus, the dual link transmitter ofthe present invention provides the important benefits of not onlytemporal alignment between the primary link data channel and thesecondary link data channel but also the important benefit of providingan aligned clock that services both the primary and secondary links.

The structure of the dual link transmitter includes both a primary linkPLL and a secondary link PLL. The primary link PLL produces a primarylink clock and the secondary link PLL produces a secondary link clock.During dual single link operations, the primary link clock is used toservice the primary link while the secondary link clock is used toservice the secondary link. However, during dual link operations, theprimary link clock is used to service both the primary link and thesecondary link.

Other features and advantages of the present invention will becomeapparent from the following detailed description of the invention madewith reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the presentinvention will be more fully understood when considered with respect tothe following detailed description, appended claims and accompanyingdrawings wherein:

FIG. 1A is a block diagram illustrating a computer and a monitor thatintercouple according to the present invention;

FIG. 1B is a system diagram illustrating a cable/satellite set top boxand a video display that intercouple according to the present invention;

FIG. 2 is a block diagram illustrating a dual link Digital VisualInterface (DVI) that operates according to the present invention;

FIG. 3 is a block diagram illustrating the elements of a dual link DVItransmitter constructed according to the present invention;

FIGS. 4A and 4B are block diagrams illustrating the structure ofencoders and serializers constructed according to the present invention;

FIG. 4C is a block diagram illustrating a DVI transmitter constructedaccording to the present invention that supports both single link anddual link mode operations;

FIG. 5 is a block diagram illustrating a phase locked loop (PLL)constructed according to the present invention;

FIG. 6A is a block diagram illustrating a bit clock temporal realignmentcircuit constructed according to the present invention;

FIG. 6B is a block diagram illustrating another embodiment of a bitclock temporal realignment circuit constructed according to the presentinvention; and

FIG. 7 is a block diagram illustrating a serializer constructedaccording to the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram illustrating a computer 100 and a monitor 102that intercouple according to the present invention. In this embodiment,the computer 100 produces visual information (and audio information insome embodiments) in the form of a high data rate bit stream that ittransmits to the monitor 102 via the serial link. As is showndiagrammatically in FIG. 1A, the computer 100 includes a transmitter Twhile the monitored 102 includes a receiver R. In one embodiment of theserial link, the DVI operating standards are substantially met, exceptas they may have been modified according to the present invention and asthey may be modified by subsequent additions/subtractions for otherpurposes. In such case, the serial link includes a physical media thatcarries a plurality of high data rate bit streams and a clock signal(bit clock). The description of the serial link provided herein refersto both single link and dual link mode operations.

FIG. 1B is a system diagram illustrating a cable/satellite set top boxand a video display that intercouple according to the present invention.As shown in FIG. 1B, a serial link couples a cable/satellite set top box104 to a video display 106. The cable/satellite set top box receivesinput via a cable/satellite input line, processes the cable/satelliteinput to produce video information, and transmits the video informationto the monitor 106 via a serial link that operates according to thepresent invention. As was the case with the description of FIG. 1A, theserial link of FIG. 1B includes may include a single link DVI or a duallink DVI, both of which are supported by both the cable/satellite settop box 104 and the video display 106.

FIG. 2 is a block diagram illustrating a dual link Digital VisualInterface (DVI) that operates according to the present invention. Thedual link DVI couples a graphics controller 202 to a display controller216. These devices may service the components of FIGS. 1A and 1B, forexample. As its output on the transmit side, the graphics controller 202produces pixel data 204 and control information 206. The pixel data 204and the control information 206 are received by a Transition MinimizedDifferential Signaling (T.M.D.S.) transmitter 208 that operatessubstantially in accordance with the DVI standard. The T.M.D.S.transmitter 208 converts the pixel data 204 and control information 206into data carried on a plurality of channels and transmits the pluralityof channels to a T.M.D.S. receiver 210. A primary link 218 of the duallink DVI includes data channel 0, data channel 1, and data channel 2. Asecondary link 220 of the dual link DVI includes data channel 3, datachannel 4, and data channel 5. A single/common clock signal (bit clock)services both the primary link 218 and the secondary link 220. Inanother embodiment, the pixel data 212 also contains audio data.

The T.M.D.S. receiver 210 receives the channels of the primary link 218and the secondary link 220 and produces pixel data 212 and controlinformation 214 based there upon. The T.M.D.S. receiver 210 provides thepixel data 212 and the control information 214 to a display controller216. The display controller 216 outputs display data and control to amonitor that creates a visual image based there upon.

According to the present invention, the T.M.D.S. transmitter 208 uses asingle Phase Locked Loop (PLL) to generate clocks used to synchronizethe transmission of both links during dual link mode operations. Usingthis technique, the bit streams of the channels of the primary link 218and the bit streams of the channels of the secondary link 220 are welltemporally aligned upon their transmission. With this superior temporalalignment, the bit stream channels arrive at the T.M.D.S. receiver 210with reduced skew, thus allowing the T.M.D.S. receiver 210 to betterreceive the channels. According to another aspect of the presentinvention, when operating as dual single links, the T.M.D.S. transmitter208 may employ dual PLLs for clock generation. A structure capable ofoperating in this manner is described with reference to FIG. 4C.

FIG. 3 is a block diagram illustrating the elements of a dual link DVItransmitter 302 constructed according to the present invention. The duallink DVI transmitter 302 includes a primary link transmitter 304, asecondary link transmitter 306, a dual link clock generator 307, and agraphics controller 308. These components may be formed in a variety ofmanners. In one embodiment, each of the components of the dual link DVItransmitter 302 are formed as a single integrated circuit. In anotherembodiment, the graphics controller 308 is formed as one integratedcircuit and the primary link transmitter 304, the secondary linktransmitter 306, and the dual link clock generator 307 are formed asanother integrated circuit. Of course, in still other embodiments, thesecomponents may be formed in other manners as well.

The graphics controller 308 couples to a host device, such as one of thehost devices illustrated in FIGS. 1A and 1B, and receives video (andaudio) data. The graphics controller 308 operates upon the video (andaudio) data to produce pixel data (and audio data) and control data. Inparticular, the graphics controller 308 produces primary link pixel (andaudio) data 310 and control data 312 that it provides to the primarylink transmitter 304. Likewise, the graphics controller 308 producessecondary link pixel (and audio) data 314 and control data 316 that itprovides to the secondary link transmitter 306.

The primary link transmitter 304 converts the primary link pixel (andaudio) data 310 and control data 312 into DATA_CH_0, DATA_CH_1, andDATA_CH_2, and LINK_1_CNTL bit streams. Likewise, the secondary linktransmitter 306 converts the secondary link pixel (and audio) data 314and control data 316 into DATA_CH_3, DATA_CH_4, and DATA_CH_5, andLINK_2_CNTL bit streams. These “channels” are transmitted to a dual linkDVI receiver contained within a receiving device. The particular formatof the “channels” produced by the dual link DVI transmitter 302 aredefined within the DVI standard and are described herein only as theyrelate to the present invention. The reader should know, however, thatthe DVI standard defines a differential signal format. Thus, the“channels” shown in FIG. 3 have a differential format event though suchformat is not explicitly shown in FIG. 3.

According to the present invention, the dual link clock generator 307receives a REF_CLK from the graphics controller 308. The dual link clockgenerator 307 uses the REF_CLK signal to produce a PRI_CLK for theprimary link transmitter 304, a SEC_CLK for the secondary linktransmitter 306, and a BIT_CLK for transmission on the dual DVI link.The BIT_CLK The structure of some components of the clock generator 307are shown in detail with reference to FIGS. 5, 6A, and 6B.

In a single link mode of operation, only the primary link or thesecondary link is operational. In a first single link mode of operationonly the primary link is operational. In a second single link mode ofoperation only the secondary link is operational. In each of thesesingle link modes of operation, the BIT_CLK includes a single componentthat services the operational link, i.e., primary link or secondarylink.

In a dual single link mode of operation, both the primary link and thesecondary link are operational but they operate independently of oneanother. In such case, the BIT_CLK includes a primary link bit clock anda secondary link bit clock. In such a mode of operation, the primarylink bit clock and the secondary link bit clock are separately generatedand may or may not be synchronized. In such case, the dual link clockgenerator 307 produces the primary link bit clock and the secondary linkbit clock separately.

In dual link mode operations, the primary link and the secondary linkare synchronized with one another. In such case, the dual link clockgenerator 307 produces and transmits a single bit clock that servicesboth the primary link and the secondary link. One particular embodimentof the dual link clock generator 307 is described with reference to FIG.4C. In the embodiment of FIG. 4C, the dual link clock generator 307includes a pair of Phase Locked Loops (PLLs). In all modes but the duallink mode, each PLL services its respective link, i.e., primary link orsecondary link. However, in the dual link mode, a single PLL of theclock generator 307 services both the primary link and the secondarylink.

FIGS. 4A and 4B are block diagrams illustrating the structure ofencoders and serializers constructed according to the present invention.FIG. 4A illustrates channel encoders and serializers that service theprimary link while FIG. 4B illustrates channel encoders and serializersthat service the secondary link. Referring now to FIG. 4A, channel 0encoder 402A and channel 0 serializer 404A receives the signalsBLU[7:0], HSYNC, VSYNC, DE (Data Enable) and PRI_CLK. The channel 0encoder 402A encodes the received data and the channel 0 serializer 404Aserializes the encoded data and transmits the data as DATA CH. 0.Likewise, the channel 1 encoder 402B and the channel 1 serializer 404Breceives the signals GRN[7:0], CTL0, CTL1, DE, and PRI_CLK. The channel1 encoder 402B encodes the received data and the channel 1 serializer404B serializes the encoded data and transmits the data as DATA CH. 1.Further, the channel 2 encoder 402C and the channel 2 serializer 404Creceives the signals RED[7:0], CTL2, CTL3, DE, and PRI_CLK. The channel2 encoder 402C encodes the received data and the channel 2 serializer404C serializes the encoded data and transmits the data as DATA CH. 2.

Referring now to FIG. 4B, secondary link components of the dual linktransmitter service the secondary link. In particular, a channel 3encoder 402D and channel 3 serializer 404D receive the signalsBLU2[7:0], CTL4, CTL5, DE (Data Enable) and SEC_CLK. The channel 3encoder 402D encodes the received data and the channel 3 serializer 404Dserializes the encoded data and transmits the data as DATA CH. 3.Likewise, the channel 4 encoder 402E and the channel 4 serializer 404Ereceives the signals GRN2[7:0], CTL6, CTL7, DE, and SEC_CLK. The channel4 encoder 402E encodes the received data and the channel 4 serializer404E serializes the encoded data and transmits the data as DATA CH. 4.Finally, the channel 5 encoder 402F and the channel 5 serializer 404Freceives the signals RED2[7:0], CTL8, CTL9, DE, and SEC_CLK. The channel5 encoder 402F encodes the received data and the channel 5 serializer404F serializes the encoded data and transmits the data as DATA CH. 5.

FIG. 4C is a block diagram illustrating a DVI transmitter constructedaccording to the present invention that supports both single link anddual link mode operations. As compared to the embodiment of FIG. 3, thedual link clock generator of FIG. 4C includes a primary link PLL 454 anda secondary link PLL 456. These PLLs 454 and 456 produce clock signalsaccording to the present invention for single link, dual single link,and dual link mode operations.

The DVI transmitter includes an input format and control block 452 thatreceives the primary link (link 0) and secondary link (link 1) data andcontrol signals from an input device, e.g., a graphics controller 308such as illustrated in FIG. 3. The input format and control block 452also receives input from the primary link PLL (PLL 0) 454 and asecondary link PLL (PLL 1) 456 that receive reference clock inputs fromthe input device. The PLL 0 454 produces the PRI_CLK and the PLL 1 456produces the SEC_CLK. A multiplexer 457 receives both the PRI_CLK andthe SEC_CLK. During single link mode operations, the PRI_CLK isgenerated by PLL 0 454 while the SEC_CLK is generated by the PLL 1 456.Each of the PRI_CLK and the SEC_CLK is used to produce a respective bitclock, TXCO+/−and TXC1+/−, respectively, that services the correspondinglink. However, during the dual link mode operations, the multiplexer 457operates such that the PLL 0 454 produces both the PRI_CLK and theSEC_CLK. The PRI_CLK is used to produce the bit clock TXCO+/−thatservices both the primary link and the secondary link during dual linkmode operations.

The primary link includes a High-Bandwidth Digital Content Protection(HDCP) engine 460, link 0 encoder 462, and serializers 464A, 464B, and464C. The secondary link includes HDCP engine 466, link 1 encoder 468,and serializers 470A, 470B, and 470C. The outputs of the serializers (aswell as the PRI_CLK and SEC_CLK signals) are differentially formed bydifferential forming elements 472. In the illustrated embodiment, thedifferential forming elements 472 are differential output operationalamplifiers.

The DVI transmitter of FIG. 4C is capable in operating in any of fourmodes: Single link 1 and single link 2 modes are identical except thatthe data and control inputs are from different sources. In these modes,only one of the two links is enabled. In the dual single link mode, bothlinks are enabled and controlled independently. In the dual link mode,the data is sourced to each link, but the two single links share thesame controls and clock, i.e., the PRI_CLK produced by PLL 0 is used toservice the secondary link components. In such case, multiplexer 457 isoperated to produce the SEC_CLK from PLL 0 454, i.e., PRI_CLK andSEC_CLK are the same signal. In dual link mode, the single transmittedbit clock, TXCO+/−, is produced from PRI_CLK and services both theprimary and the secondary links.

FIG. 5 is a block diagram illustrating a phase locked loop (PLL)constructed according to the present invention. The PLL includes a phasedetector 502 that receives the REF_CLK produces by an input device andcompares the phase of the REF_CLK to a low speed PLL output(LS_PLL_OUTPUT) produced by a divide by ten counter 506. A loop filter505 receives the output of the phase detector 502, filters the output,and produces a filtered output as the input to a Voltage ControlledOscillator (VCO) 505. The VCO 505 produces a high speed PLL output(HS_PLL_OUTPUT) that also serves as the input to the divide by tencounter 506.

FIG. 6A is a block diagram illustrating a bit clock temporal realignmentcircuit constructed according to the present invention. The bit clocktemporal realignment block 600 includes a D flip flop 602 that receivesthe LS_PLL_OUTPUT as its data input and the HS_PLL_OUTPUT as its CLKinput. The bit clock temporal realignment block 600 produces the BIT_CLKas its output. The bit clock is also referred to as the PRI_CLK in FIG.4C prior to its conversion to a differential signal.

FIG. 6B is a block diagram illustrating another embodiment of a bitclock temporal realignment circuit 652 constructed according to thepresent invention. The bit clock temporal realignment circuit 652receives the HS_PLL_OUTPUT signal and produces the BIT_CLK (PRI_CLK).The bit clock temporal realignment circuit 652 includes a divide by tencounter 654 that receives the HS_PLL_OUTPUT signal and that produces thedata input to a D flip flop 656. The D flip flop 656 is clocked by theHS_PLL_OUTPUT signal and produces the bit clock.

FIG. 7 is a block diagram illustrating a serializer constructedaccording to the present invention. The serializer includes a parallelto serial converter 702 and a data alignment circuit 704. The parallelto serial converter 702 receives a parallel data signal DATA[7:0] thatis eight bits wide and converts the parallel data signal a bit streambased upon the LS_PLL_OUTPUT and/or the HS_PLL_OUTPUT, depending uponthe particular embodiment employed. The bit stream produced by theparallel to serial converter 702 is received by the data alignmentcircuit 704 that temporally aligns the bit stream to produce atemporally aligned bit stream as channel 0, for example. Each of the sixchannels of a dual link transmitter constructed according to the presentinvention includes a data alignment circuit so that the channel dataoutput will be temporally aligned with the BIT_CLK produced by thetransmitter. In order to temporally align the data channels with theBIT_CLK, the data alignment circuit 704 uses the LS_PLL_OUTPUT and/orthe HS_PLL_OUTPUT.

The invention disclosed herein is susceptible to various modificationsand alternative forms. Specific embodiments therefore have been shown byway of example in the drawings and detailed description. It should beunderstood, however, that the drawings and detailed description theretoare not intended to limit the invention to the particular formdisclosed, but on the contrary, the invention is to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the present invention as defined by the claims.

1-27. (canceled)
 28. An apparatus comprising: a primary link transmitterhaving a plurality of primary link data channels to transmit encoded andserialized primary link data; a secondary link transmitter having aplurality of secondary link data channels to transmit encoded andserialized secondary link data; and a clock generator coupled to theprimary link transmitter and to the secondary link transmitter togenerate a primary clock signal and a secondary clock signal, whereinduring a single link mode of operation the primary clock signal is usedas a primary link bit clock for the primary link data channels and thesecondary clock signal is selected as a secondary link bit clock for thesecondary link data channels, but during a dual link mode of operationthe primary clock signal is used as the primary link bit clock for theprimary link data channels and also selected as the secondary link bitclock for the secondary link data channels to ensure synchronization ofdata on the primary link data channels and the secondary link datachannels.
 29. The apparatus of claim 28, wherein the clock generatorincludes a primary link Phase Locked Loop (PLL) to generate the primaryclock signal and a secondary link PLL to generate the secondary clocksignal.
 30. The apparatus of claim 29 further comprising a multiplexerto select between the primary clock signal and the secondary clocksignal for coupling to the secondary link transmitter.
 31. The apparatusof claim 28, wherein: the primary link transmitter includes a pluralityof primary link data channel temporal alignment blocks to align bits ofthe primary link data channel with the primary link bit clock; and thesecondary link transmitter includes a plurality of secondary link datachannel temporal alignment blocks to align bits of the secondary linkdata channel with the secondary link bit clock.
 32. The apparatus ofclaim 28, wherein: the primary link transmitter further includes a firstHigh-Bandwidth Digital Content Protection engine; and the secondary linktransmitter further includes a second High-Bandwidth Digital ContentProtection engine.
 33. The apparatus of claim 28, wherein the datatransmitted on the primary and secondary data channels are compliantwith a particular digital standard.
 34. The apparatus of claim 33,wherein the particular digital standard is a Digital Visual Interfacestandard.
 35. An apparatus comprising: a primary link transmitter havinga plurality of primary link data channels to transmit encoded andserialized primary link data; a secondary link transmitter having aplurality of secondary link data channels to transmit encoded andserialized secondary link data; a secondary link Phase Locked Loop (PLL)to generate a secondary clock signal which is used by the secondary linktransmitter as a secondary link bit clock for the secondary link datachannels during a single link mode of operation; and a primary link PLLto generate a primary clock signal which is used by the primary linktransmitter as a primary link bit clock for the primary link datachannels during the single link mode of operation, but the primary clocksignal is coupled to both the primary link transmitter and the secondarylink transmitter during a dual link mode of operation and to be used asthe primary link bit clock and the secondary link bit clock tosynchronize data on the primary link data channels and the secondarylink data channels.
 36. The apparatus of claim 35 further comprising amultiplexer to select between the primary clock signal and the secondaryclock signal for coupling to the secondary link transmitter.
 37. Theapparatus of claim 35, wherein: the primary link transmitter includes aplurality of primary link data channel temporal alignment blocks toalign bits of the primary link data channel with the primary link bitclock; and the secondary link transmitter includes a plurality ofsecondary link data channel temporal alignment blocks to align bits ofthe secondary link data channel with the secondary link bit clock. 38.The apparatus of claim 35, wherein: the primary link transmitter furtherincludes a first High-Bandwidth Digital Content Protection engine; andthe secondary link transmitter further includes a second High-BandwidthDigital Content Protection engine.
 39. The apparatus of claim 35,wherein the data transmitted on the primary and secondary data channelsare compliant with a particular digital standard.
 40. The apparatus ofclaim 39, wherein the particular digital standard is a Digital VisualInterface standard.
 41. A method comprising: generating a primary clocksignal; generating a secondary clock signal; using the secondary clocksignal as a secondary link bit clock to transmit encoded and serializedsecondary link data on a plurality of secondary link data channelsduring a single link mode of operation; and using the primary clocksignal as a primary link bit clock to transmit encoded and serializedprimary link data on a plurality of primary link data channels duringthe single link mode of operation, but during a dual link mode ofoperation, using the primary clock signal as both the primary link bitclock and the secondary link bit clock to synchronize dual link data onthe primary link data channels and the secondary link data channels. 42.The method of claim 41, wherein generating the primary clock signalincludes generating a phase locked loop clock signal.
 43. The method ofclaim 42, further comprising transmitting data on the primary andsecondary data channels that are compliant with a particular digitalstandard.
 44. The method of claim 43, wherein the particular digitalstandard is a Digital Visual Interface standard.